The present invention is generally related to monitoring and controlling a fluid transportation system. More specifically, the present invention is directed to a controller having a flow meter module for monitoring and controlling a fluid flow volume in a fluid transportation system.
The production, transportation and sale of energy products has always required some form of measurement to determine the quantity produced, bought or sold. The accuracy and reliability of a system that measures an energy product, i.e., gas and liquid, is extremely important to the buyers and sellers involved. A seemingly insignificant error within the measuring system can result in extensive monetary losses.
Technological advances in the areas of fluid flow metering and computation has led to improved accuracy and reliability. Some of these advances have been made in the area of metering, or measuring, transported energy products. These advances have also focused on factors such as safety, reliability and standardization.
Today""s metering and transfer system involves more than simply measuring fluid flow; it can also involve extensive electronics, software, communications interfaces, analysis and control. Measuring fluid flow includes multiple turbine meters with energy flow computers, densitometers, gas chromatography, meter-proving systems and RTU or SCADA interfaces. Measurement and control of energy sources is a valuable process for companies producing and transporting energy sources. Many governments, organizations and industries have enacted standards and regulations related to the recovering, refining, distributing and selling of oil and oil by-products, i.e., gasoline, kerosene, butane, ethanol, etc. The energy resource industry has various standards and regulations to ensure the accuracy and safety of transporting and metering these energy sources.
The process of transporting fluid, typically oil, through a pipeline is monitored and controlled with the assistance of a combination of sensors and process computers. Generally, a computer processor monitors the several aspects of the oil transportation, such as fluid flow volume. The control of the equipment facilitating the transportation of oil is generally performed by environmentally robust devices such as a controller. The controller regulates valves, tanks and scales without requiring an individual to constantly interact with the system.
A very important aspect of a fluid transportation system involves the fluid flow meters utilized to monitor the amount of oil delivered to a customer. Because of the vast amounts of fluid delivered, the accuracy of the fluid flow meter must be ensured at regular intervals. An inaccurate fluid flow meter can result in overcharging or undercharging a customer for the delivered product.
A turbine flow meter is an accurate and reliable flow meter for both liquids and gas volumetric flow. Some applications utilizing a turbine flow meter involve water, natural gas, oil, petrochemical, beverage, aerospace, and medical. The turbine comprises a rotor having a plurality of blades mounted across the flow direction of the fluid. The diameter of the rotor is slightly less than the inner diameter of the conduit, and its speed of rotation is proportional to the volumetric flow volume. Turbine rotation can be detected by solid-state devices or mechanical sensors.
In one application incorporating a variable reluctance coil pick-up, a coil is a permanent magnet and the turbine blades are made of a material attracted to a magnet. As each blade passes the coil, a voltage pulse is generated in the coil. Each pulse represents a discrete volume of liquid. The number of pulses per unit volume is called the meter""s K-factor.
In another application utilizing inductance pick-up, a permanent magnet is embedded in the rotor. As each blade passes the coil, a voltage pulse is generated. Alternatively, only one blade is magnetic and the pulse represents a complete revolution of the rotor. Depending upon the design, it may be preferable to amplify the output signal prior to its transmission.
Proving the fluid flow meter is a process for ensuring the accuracy of the flow meter. Typically, a section of the fluid system called a proving loop is utilized during the meter proving. The dimensions of the proving loop are known and the flow of fluid within the loop can be monitored by sensors wherein a variety of fluid characteristics can be sensed. The meter-proving process simultaneously monitors a pulse signal generated by a turbine operably connected within the fluid system. The flow volume of the fluid is determined by utilizing the sensed values with industrial standard flow volume equations, e.g., American Gas Association and American Petroleum Institute standard equations. The calculated flow volume is then compared to the known flow volume of the proving loop. By comparing the calculated fluid flow volume to the known fluid flow volume of the proving loop, the accuracy of the flow meter can be determined.
The duration of a meter-proving process is generally one-hundred-thousand turbine pulses. This amount of time is believed to be adequate to accurately determine the fluid flow volume. Generally, the turbine pulse signal is not in synch with the flow meter proving process, i.e., the meter proving process will generally not start at the beginning of the turbine pulse signal. When the pulses are counted at the end of the proving period, the partial pulses occurring at the beginning and end of the proving period are omitted. Because of the duration of the proving period, it is generally believed that these partial pulses are negligible. However, utilizing the partial pulses and other characteristics of the monitored fluid can reduce the time required for the meter proving process, thus reducing the length of the proving loop.
This invention is directed to solving these and other problems.
The present invention is directed to utilizing a controller to monitor a flow volume in a fluid transportation system. The controller, preferably a programmable logic controller, cooperates with a flow meter to sense a fluid and determine a flow volume. The controller also ensures the accuracy of the flow meter using an interpolation method. As a result, a less expensive implementation of monitoring a fluid transportation system with a controller can be realized.
An embodiment of the present invention is directed to a method of proving a flow meter. The flow meter is connected to a controller and a proving loop within a fluid transportation system. The proving loop has a known flow volume. The controller monitors a fluid flow within the proving loop. The method comprises the steps of starting a meter-proving period and sensing a pulse signal responsive to a flow meter. The flow meter generates a fluid flow through the fluid transportation system. The meter-proving process is terminated and the amount of sensed pulse signals occurring during the meter-proving period is calculated. The fluid flow volume of the proving loop is determined in response to the pulse signals occurring during the meter-proving process and other sensed characteristics, preferably density, of the fluid. The calculated flow volume of the proving loop is compared against the known volume of the proving loop. The meter-proving process is executed within the controller.
The calculation of the sensed pulse signals is the sum of the full pulse signals and the partial pulse signals occurring during the meter-proving process. The partial pulse signals are interpolated to provide an accurate pulse signal measurement.
A further aspect of the above embodiment of the present invention is directed to adjusting the flow meter and/or controller in response to the comparison of the calculated flow volume of the proving loop and its known flow volume, wherein the fluid flow meter and/or controller more accurately calculate the flow volume.
A further embodiment of the present invention is directed to method of measuring a flow volume of a fluid within a conduit. A controller is connected to a flow meter and the conduit. The controller monitors the fluid flow volume through a plurality of input channels operably connected to the flow meter of a fluid transportation system. The controller senses a pulse signal generated by the flow meter over a period of time determined by the size of the meter-proving loop. A densitometer being operably connected to the controller senses the real time density of the fluid. The density of the fluid is sensed and stored by the controller as a dynamic variable to be utilized in the determination of the flow volume. The controller utilizes the sensed dynamic density in cooperation with an industrial standard, API 2540, which yields a correction factor, M, to be used by another standard industrial equation, AGA-7, for calculating a flow volume through the measuring flow meter.
Significant cost savings can be attained by implementing a less expensive controller capable of performing the monitoring and control functionality required for determining a flow volume. In addition, more accurate flow volume calculations can be obtained by utilizing additional characteristics, i.e., real time density values, in cooperation with the industrial standard equations.
Other advantages and aspects of the present invention will become apparent upon reading the following description of the drawings and detailed description of the invention.